Optical probe and optical tomography system

ABSTRACT

An optical probe includes a tubular outer envelope and a optical fiber which extends in the longitudinal direction of the outer envelope inside the outer envelope. By fixing a light deflecting element to the optical fiber and rotating the optical fiber by a driver, the light deflecting element is rotated. A protective member which has a higher resistance to wear than the outer peripheral surface of the optical fiber is fixed to a part of the outer peripheral surface of the optical fiber in a position near the front end of the optical fiber and is borne for rotation by a bearing portion on the probe outer envelope.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical probe, and more particularly to anoptical probe having a tubular outer envelope and having a function ofdeflecting light emitted from the peripheral surface thereof in thedirection of circumference or the axis of the outer envelope. Thepresent invention also relates to an optical tomography system wheresuch an optical probe is employed.

2. Description of the Related Art

As a conventional method for obtaining tomographic images of measurementtargets, such as living tissue, a method that obtains opticaltomographic images by OCT (Optical Coherence Tomography) measurement hasbeen proposed (refer to Japanese Unexamined Patent Publication Nos.6(1994)-165784 and 2003-139688). The OCT measurement is a type of lightinterference measurement method that utilizes the fact that lightinterference is detected only when the optical path lengths of dividedlight beams, that is, a measurement light beam and a reference lightbeam, match within a range of coherence length of a light source. Thatis, in this method, a low coherent light beam emitted from a lightsource is divided into a measuring light beam and a reference lightbeam, the measuring light beam is irradiated onto a measurement target,and the measurement light beam reflected by the measurement target isled to a multiplexing means. Whereas the reference light beam is led tothe multiplexing means after its optical path length is adjusted so thatits optical path length equalizes to that of the reflected light from anarbitrary position in the object. Then the measuring light and thereference light is multiplexed by the multiplexing means, and theintensities thereof are detected by the light detector.

In order to obtain a one-dimensional tomographic image, an interferencestrength waveform according to the reflectance distribution along thesame axis as the direction of travel of the measuring light by scanningthe optical path length of the measuring light according to themeasuring area. That is, a reflected light intensity distributionaccording to the structure in the direction of depth of the object to bemeasured can be obtained. Further, when the projecting position of themeasuring light applied to the object is one-dimensionally scanned in adirection perpendicular to the optical axis by the use of a deflectingmeans or a physical means, a two dimensional tomography representing areflected light intensity distribution can be obtained. Further, whenthe projecting position of the measuring light is two-dimensionallyscanned in directions perpendicular to the optical axis, a threedimensional tomography representing a reflected light intensitydistribution can be obtained.

In the above OCT system, a tomographic image is obtained by changing theoptical path length of the reference light, thereby changing themeasuring position (the depth of measurement) in the object. Thistechnique is generally referred to as “TD-OCT (time domain OCT)”. Morespecifically, in the optical path length changing mechanism for thereference light disclosed in Japanese Unexamined Patent Publication No.6 (1994)-165784, an optical system which collects the reference lightemitted from the optical fiber on a mirror is provided and the opticalpath length is adjusted by moving only the mirror in the direction ofthe optical axis of the reference light. Further, in the optical pathlength changing mechanism for the reference light disclosed in JapaneseUnexamined Patent Publication No. 2003-139688, the reference lightemitted from the optical fiber is turned to parallel light by a lens,the reference light in the form of parallel light is collected andcaused to enter the optical fiber again by an optical path lengthadjusting lens, and the optical path length adjusting lens is moved backand forth in the direction of the beam axis of the reference light.

Whereas, as a system for rapidly obtaining a tomographic image withoutchanging the optical path length of the reference light, there has beenproposed an optical tomography system for obtaining an opticaltomographic image by measurement of SD-OCT (spectral domain OCT). In theSD-OCT system, a tomographic image which is one-dimensional in theoptical axis is formed without physically scanning the optical pathlength, by dividing broad band, low coherent light into measuring lightand reference light by the use of an interferometer as in theabove-described TD-OCT system, substantially equalizing the measuringlight and the reference light to cause them to interfere with eachother, decomposing the interference light into the optical frequencycomponents, measuring the intensity of the interference light by theoptical frequency components by an array type detector and carrying outa Fourier analysis on the obtained spectral interference waveforms by acomputer. As in above-described TD-OCT system, a two-dimensional or athree-dimensional tomographic image can be obtained by scanning theprojecting position of the measuring light in directions perpendicularto the optical axis.

As another system for rapidly obtaining a tomographic image withoutchanging the optical path length of the reference light, there has beenproposed an optical tomography system for obtaining an opticaltomographic image by measurement of SS-OCT (swept source OCT). TheSS-OCT system employs a light frequency tunable laser as a light source,The high coherence laser beam is divided into measuring light andreference light. The measuring light is projected onto the object andthe reflected light from the object is led to the multiplexing means.The reference light is led to the multiplexing means after it is madesubstantially equal to the measuring light in the optical path length tocause the measuring light and the reference light to interfere with eachother, and the measuring light and the reference light are multiplexedby the multiplexing means. The intensity of the multiplexed light isdetected by an optical detector. The intensity of the interference lightis measured by the frequency component by sweeping the frequency of thelight frequency tunable laser and a one-dimensional tomography in theoptical axis is formed without physically scanning the optical pathlength by Fourier-transforming the spectral interference waveform thusobtained with a computer. As in above-described TD-OCT system, atwo-dimensional or a three-dimensional tomographic image can be obtainedby scanning the projecting position of the measuring light in directionsperpendicular to the optical axis.

In the optical tomography system of each of the systems described above,a tomographic image along a certain surface of the object is generallyobtained and for this purpose, it is necessary to at leastone-dimensionally scan the measuring light beam in the object inperpendicular to the optical axis. As a means for effecting such a lightscanning, there has been known, as disclosed in Japanese Patent No.3104984, an optical probe having a tubular outer envelope and having afunction of deflecting light emitted from the peripheral surface thereofin the direction of circumference of the outer envelope. Morespecifically, the optical probe comprises an inserting portion (outerenvelope) which is inserted into the sample, a rotatable hollow shaftwhich is inserted inside the outer envelope, an optical fiber which ispassed through the shaft, and a light deflecting element which isconnected to the front end portion of the shaft to be rotated togethertherewith and deflects light radiated from the front endportion of theoptical fiber in a direction of circumference of the outer envelope.

Observing an optical tomographic image has been expected to be developedfrom the digestive organ which has been reported in the past to a finerregion such as a bronchus, a ureter, and a blood vessel. From such aviewpoint, it has been required to make thinner the optical probe.However, in the optical probe disclosed in Japanese Patent No. 3104984,it is necessary to have a certain wall thickness to ensure the strengthof the shaft and to ensure a space between the shaft and the opticalfiber inside thereof, which makes difficult to make thinner the opticalprobe.

There is a further demand that a deeper region of the object is to beobserved. However, to realize this, it is necessary to make a probe aslong as several meters, and it is very difficult to pass an opticalfiber through the inside of a shaft which is cylindrical and elongated.Further, the optical fiber can be damaged when it is passed through theinside of such a shaft and accordingly, use of such a probe deterioratesthe productivity. Further, since such a cylindrical shaft is high in itsmanufacturing cost, the optical probe is high in cost. when the opticalfiber is rigid, it is conceivable not to pass the optical fiber throughthe shaft described above and to rotate together with a light deflectingelement fixed to the tip of the optical fiber. However, in this case, itis necessary to set a space between the optical fiber and the innerperipheral surface of the outer envelope of the probe in order tosmoothly rotate the optical fiber and in such a structure, it is notavoidable the front end the end of the optical fiber wobbling. When so,the orbit of the deflected light emitted from the optical probe isdisturbed and it is impossible to construct an accurate tomographicimage in the sample.

SUMMARY OF THE INVENTION

In view of the foregoing observations and description, the primaryobject of the present invention is to provide an optical probe which iseasy to make thin, can be produced at low cost and at the same time thelight emitted from the outer peripheral surface of the outer probe ofthe optical probe is orderly deflected to generate an orbit in a plane.

Another object of the present invention is to provide an opticaltomography system which can be miniaturized and can be manufactured atlow cost by the use of such an optical probe.

In accordance with the present invention, the above objects areaccomplished by avoiding a complicated structure of passing a hollowshaft through the outer envelope of the optical probe and passing anoptical fiber through the shaft, employing a structure where the opticalfiber is rotated in the probe outer envelope and then causing a bearingportion provided outside the probe outer envelope to bear the opticalfiber for rotation.

More specifically, in accordance with the present invention, there isprovided an optical probe comprising

a tubular outer envelope,

a optical fiber which extends in the longitudinal direction of the outerenvelope inside the outer envelope,

a drive means which rotates the optical fiber in the circumferentialdirection of the outer envelope,

a light deflecting element which is integrally held to rotate togetherwith the optical fiber and deflects light emitted from a front end ofthe optical fiber,

a light collecting means which collects light emitted from the front endof the optical fiber and converges it on a body-to-be-scanned disposedexternally of the circumference of the outer envelope,

a protective member which has a higher resistance to wear than the outerperipheral surface of the optical fiber, and is fixed to a part of theouter peripheral surface of the optical fiber in a position near thefront end of the optical fiber, and

a bearing portion which is fixed to the inner peripheral surface of theprobe outer envelope to bear for rotation the optical fiber by way ofthe protective member

The outer side of the clad of the optical fiber is generally providedwith a coating formed of resin such as ultraviolet setting resin. Insuch a case, the outer peripheral surface of the optical fiber is formedby the resin. In this case, the protective member which has a higherresistance to wear than the outer peripheral surface of the opticalfiber is formed of metal such as stainless steel.

Further, the protective member may be provided with an abutment portionwhich abuts against a part of the bearing portion to suppress themovement of the protective member in the direction of axis of theoptical fiber.

The tomography system of the present invention is characterized in thatthe optical probe of the present invention is employed in each of theabove described various systems of the optical tomography systems. Thatis, in accordance with the present invention, there is provided anoptical tomography system for obtaining a tomographic image of an objectto be measured comprising

a light source which emits light,

a light dividing means which divides light emitted from the light sourceinto measuring light and reference light,

a projecting optical system which projects the measuring light onto theobject,

a multiplexing means which multiplexes the reflected light from theobject when the measuring light is projected onto the object and thereference light,

an interference light detecting means which detects interference lightof the reflected light and the reference light which have beenmultiplexed by the multiplexing means, and

a tomographic image obtaining means which detects intensities of theinterference light in positions in the direction of depth of the objecton the basis of the frequency and intensity of the detected interferencelight and obtains a tomographic image of the object on the basis of theintensity of the reflected light in each position of the depth,

wherein the improvement comprises that the projecting optical systemincludes an optical probe of the present invention.

The optical probe in accordance with the present invention, since anoptical fiber disposed in the outer envelope of the probe holds thelight deflecting element and the optical fiber is rotated to rotate thelight deflecting element, can be very simpler in structure as comparedwith the conventional optical probe where a hollow shaft is passedthrough the outer envelope of the probe and an optical fiber is passedthrough the shaft. Accordingly, the optical probe of the presentinvention is easy to make thin and can be manufactured at low cost.

Further, since in the optical probe in accordance with the presentinvention, an optical fiber is disposed in the outer envelope of theprobe, the optical fiber cannot be very difficult to dispose even if theoptical probe is substantially long unlike the case where the hollowshaft intervenes therebetween. Accordingly, the manufacturing cost canbe low,

Even if the optical fiber is directly disposed in the outer envelope asdisclosed above, the optical fiber cannot be rotated with its front endwobbling, since the optical fiber is supported for rotation by thebearing portion on the probe outer envelope. Thus in accordance with theoptical probe, the light emitted from the outer peripheral surface ofthe outer probe of the optical probe is orderly deflected to generate anorbit in a plane.

Further, since the optical fiber is borne by way of the protectivemember which has a higher resistance to wear than the outer peripheralsurface of the optical fiber, the outer peripheral surface of therotating optical fiber is prevented from being worn out by friction withthe inner peripheral surface of the probe outer envelope.

When the protective member is provided with an abutment portion whichabuts against a part of the bearing portion to suppress the movement ofthe protective member in the direction of axis of the optical fiber, theprotective member is prevented from being separated from the bearingportion, whereby the optical fiber can be prevented from being rotatedwith the protective member being separated from the bearing portion sothat the outer peripheral surface of the optical fiber and/or the lightdeflecting element is rubbed against the inner peripheral surface of theprobe outer envelope to be damaged or to be worn out.

Further, since the optical probe of the present invention is applied,the optical tomography system of the present invention can beminiaturized and can be manufactured at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view showing an optical probe inaccordance with a first embodiment of the present invention,

FIG. 2 is a front cross-sectional view of the optical probe of FIG. 1,

FIG. 3 is a perspective view of an optical tomographic system to whichthe optical probe of FIG. 1 is applied,

FIG. 4 is a side cross-sectional view showing an optical probe inaccordance with a second embodiment of the present invention,

FIG. 5 is a schematic view showing an example of the optical tomographysystem by the SD-OCT measurement to which the optical probe of thepresent invention is applied,

FIG. 6 is a schematic view showing an example of the optical tomographysystem by the SS-OCT measurement to which the optical probe of thepresent invention is applied, and

FIG. 7 is a schematic view showing an example of the optical tomographysystem by the TD-OCT measurement to which the optical probe of thepresent invention is applied.

DESCRIPTION OF THE PREFERRED EMBODIMNTS

Embodiments of the present invention will be described in detail withreference to the drawings, hereinbelow. FIG. 1 shows a sidecross-sectional shape of an optical probe 10 in accordance with a firstembodiment of the present invention and FIG. 2 is a frontcross-sectional view of the optical probe 10 taken along line A-A inFIG. 1. For example, the optical probe 10 forms a front end portion ofan endoscope which forms a part of an optical tomography system. FIG. 3shows an entire shape of the optical tomography system.

The optical tomography system will be first described in brief withreference to FIG. 3. The system comprises an endoscope 50 including theoptical probe 10; a light source unit 51, a video processor 52, and anoptical tomographic processing system 53 to which the endoscope 50 isconnected; and a monitor 54 connected to the video processor 52. Theendoscope 50 comprises an outer envelope 11 which is flexible andelongated, a control portion 56 connected to the rear end of theendoscope outer envelope 11 and a universal code 57 which extendsoutward from a side portion of the control portion 56.

A light guide (not shown) which transmits illuminating light from thelight source unit 51 is passed through the universal code 57, and alight source connector 58 which is removably connected to the lightsource unit 51 is provided on the end of the universal code 57. A signalcable 59 extends from the light source connector 58 and a signalconnector 60 which is removably connected to the video processor 52 isprovided on the end of the signal cable 59. The light source unit 51 isfor projecting the illuminating light onto a part of a sample 70 atomographic image of which is to be obtained as described later.

A bight control knob 61 for controlling a bight portion provided in theprobe outer envelope 11 and a light guide drive portion 62 are providedon the control portion 56, and the light guide drive portion 62 and theoptical tomographic processing system 53 are connected to each other byway of a light guide 63. The probe outer envelope 11 is inserted intothe sample 70 such as a human organ.

The optical probe 10 will be described with reference to FIGS. 1 and 2,hereinbelow. The optical probe 10 comprises: a cylindrical probe outerenvelope 11 having a closed front end; an annular bearing portion 12fixed to a part of the inner peripheral surface of the outer envelope11; a single optical fiber 13, which is provided inside the outerenvelope 11 to extend in the direction of the axis of the outer envelope11; and a gear 14 a fixed to a part of the outer peripheral surface ofthe optical fiber 13, a gear 14 b in mesh with the gear 14 a and a motor15 which rotates the gear 14 b.

A cylindrical protective member 16 is fixed to a part of the probe outerenvelope 11 near the front end thereof and the protective member 16 isborne for rotation by the bearing portion 12. Accordingly, when themotor 15 is driven, the optical fiber 13 is rotated about itslongitudinal axis in the circumferential direction of the probe outerenvelope 11 by way of the gears 14 a and 14 b. In this embodiment, thegears 14 a and 14 b and the motor 15 form a drive means for rotating theoptical fiber 13.

The protective member 16 is made of material which is higher inresistance to wear than the outer peripheral surface of the opticalfiber 13. When the optical fiber 13 has a core 13 a and a clad 13 b, anda coating 13 c formed of resin such as ultraviolet setting resin isprovided on the outer peripheral surface of the clad 13 b as shown inFIG. 2, the outer peripheral surface of the optical fiber 13 is formedby resin. In this case, the protective member is made of metal such asstainless steel higher in resistance to wear than resin or resin such asTeflon® having a high resistance to wear. Though not shown, the opticalfiber 13 is provided with a similar protective member fixed in aposition near to the gear 14 a and the protective member is borne forrotation by a bearing portion similar to the bearing portion 12.

The optical probe 10 is further provided with a rod lens 18 fixed to thefront end of the optical fiber 13 and a prism mirror 17 fixed to the rodlens 18, The prism mirror 17 is rotate together with the optical 13 todeflect by 900 light L emitted from the front end of the optical fiber13 in the circumferential direction of the probe outer envelope 11, anda rod lens 18 which collects light L emitted from the front end of theoptical fiber 13 to converge on the sample 70 as the object to bescanned which is disposed externally of the circumference of the outerenvelope 11. In this particular embodiment, the rod lens 18 and theprism mirror 17 double as a light-guide means which leads the light Lreflected by the sample 70 to the front end of the optical fiber 13 toenter the optical fiber 13 from the front end as will be describedlater.

An incident optical system 20 is disposed inside the endoscope 50 to beopposed to the base end of the optical fiber 13 as shown in FIG. 3.Light L propagating the light guide 63 and emitted from the light guide63 is collected by the incident optical system 20 and enters the opticalfiber 13 from the base end thereof.

Operation of the optical probe 10 will be described, hereinbelow. Alight source such as a laser (not shown) is disposed in the opticaltomographic processing system 53 shown FIG. 3, and the light L such as alaser beam emitted therefrom enters the light guide 63 and propagatestherethrough. The light L entering the optical fiber 13 by way of theincident optical system20 after emitted from the light guide 63propagates through the optical fiber 13, is emitted from the front endthereof, is reflected by 90° by the prism mirror 17 after collected bythe rod lens 18 and is emitted outside the probe 10 through the outerenvelope 11 which is light-transmittable. Then when the motor 15 isdriven, the optical fiber 13 rotates as described above and the prismmirror 17 and the rod lens 18 fixed thereto are rotated together withthe optical fiber 13.

In response to rotation of the prism mirror 17, the light L emittedtherefrom is deflected in the circumferential direction of the probeouter envelope 11, thereby scanning the sample 70 in the direction ofarrow R in FIG. 3. The light L is reflected by the sample 70 whilescattering and a part of the reflected light impinges upon the prismmirror 17 and is reflected toward the rod lens 18. The part of thereflected light is collected by the rod lens 18 and enters the opticalfiber 13 from the front end thereof.

The reflected light thus propagating through the optical fiber 13 isemitted from the base end of the optical fiber 13, enters the lightguide 63 by way of the incident optical system 20 shown in FIG. 3, andpropagates through the light guide 63 to be transmitted to the opticaltomographic processing system 53. In the optical tomographic processingsystem 53, the above described reflected light is branched from theoptical path of the light L to the optical probe 10, and is detected byan optical detector (not shown). A tomographic image of the sample 70 isformed on the basis of the output of the optical detector and thetomographic image is displayed on the monitor 54 shown in FIG. 3.

As can be understood from the description above, the optical probe 10 ofthis embodiment, where the optical fiber 13 is disposed in the probeouter envelope 11 and the optical fiber 13 is rotated to rotate theprism mirror 17 as the light deflecting element, can be very simpler instructure as compared with the conventional optical probe where a hollowshaft is passed through the outer envelope of the probe and an opticalfiber is passed through the shaft. Accordingly, the optical probe 10 iseasy to make thin and can be manufactured at low cost.

Further, since in the optical probe 10 of this embodiment, an opticalfiber 13 is directly disposed in the outer envelope 11 of the probe 10,the optical fiber 13 cannot be very difficult to dispose even if theoptical probe 10 is substantially long unlike the case where the hollowshaft intervenes therebetween. Accordingly, the manufacturing cost canbe low.

Even if the optical fiber 13 is directly disposed in the outer envelope11 as disclosed above, the-optical fiber 13 cannot be rotated with itsfront end wobbling, since the optical fiber 13 is supported for rotationby the bearing portion 12 on the probe outer envelope 11. Thus inaccordance with the optical probe 10, the light emitted L from the outerperipheral surface of the outer probe 11 of the optical probe 10 can beorderly deflected to generate an orbit in a plane.

Further, since the optical fiber 13 is borne by way of the protectivemember 16 which has a higher resistance to wear than the outerperipheral surface of the optical fiber 13, the outer peripheral surfaceof the rotating optical fiber 13 is prevented from being worn out byfriction with the inner peripheral surface of the probe outer envelope11.

A second embodiment of the present invention will be described,hereinbelow. FIG. 4 is a side view partly cut away of an optical probe100 in accordance with the second embodiment of the present invention.In FIG. 4, the elements analogous to those in FIGS. 1 to 3 are given thesame reference numerals and will not be described unless necessary. (thesame in the following drawings) The optical probe 100 of the secondembodiment differs from that 10 of the first embodiment in that aprotective member 16′ having a pair of abutment portions 16 a is used inplace of the protective member 16.

The protective member 16′ is disposed so that the pair of abutmentportions 16 a on the respective sides of the bearing portion 12. Theabutment portions 16 a have an outer diameter between the inner diameterand the outer diameter of the bearing portion 12. When the protectivemember 16′, that is, the optical fiber 13 tends to move in the axialdirection of the optical fiber 13, one of the abutment portions 16 aabuts against the corresponding end surface of the bearing portion 12and inhibits the movement of the optical fiber, whereby the opticalfiber 13 can be prevented from being rotated with the protective member16′ being separated from the bearing portion 12 so that the outerperipheral surface of the optical fiber 13 and/or the prism mirror 17 isrubbed against the inner peripheral surface of the probe outer envelope11 to be damaged or to be worn out.

The bearing 12 may be in plurals without being limited to a single asdescribed above. Further, it is possible to dispose a plurality ofoptical fibers 13 to rotate them together. Grease may be providedbetween the bearing portion 12 and the protective layer 16 or 16′ torotate the optical fiber 13 more smoothly. Further, the inner space ofthe probe outer envelope 11 may be filled with a high viscosity fluidsuch as oil.

In the embodiment described above, the prism mirror 17 which is thelight deflecting element and the rod lens 18 which is the lightcollecting means are disposed in close contact with each other. However,this is not essential but the prism mirror 17 and the rod lens 18 may bespaced from each other. Positions of the light deflecting element andthe light collecting means along the optical axis in the aboveembodiments may be reversed and the light deflecting element may bepositioned on the side nearer to the light source.

Examples of the optical tomography system to which the optical probes ofthe present invention are to be applied will be described, hereinbelow.The optical tomography system 1 shown in FIG. 5 is for obtaining atomographic image of an object of measurement such as a living tissue ora cell in a body cavity by measuring the SD-OCT. The optical tomographysystem 1 comprises: a light source unit 210 which emits light La; alight dividing means 3 which divides the light La emitted from the lightsource unit 210 into measuring light L1 and reference light L2; anoptical path length adjusting means 220 which adjusts the optical pathlength of the reference light L2 divided by the light dividing means 3;an optical probe 10 which guides to the object Sb to be measured themeasuring light beam L1 divided by the light dividing means 3; amultiplexing means 4 for multiplexing a reflected light beam L3 from theobject Sb when the measuring light beam L1 is irradiated onto the objectSb from the probe 10, and the reference light beam L2; and aninterference light detecting means 240 for detecting interference lightbeam L4 of the reflected light beam L3 and the reference light beam L2which have been multiplexed by the multiplexing means 4.

The light source unit 210 comprises a light source 111 which emits lowcoherence light La such as an SLD (super luminescent diode), ASE(amplified spontaneous emission) or a super continuim where an ultrashort pulse laser beam is projected onto a nonlinear medium to obtainbroad band light and an optical system 112 which enters the lightemitted from the light source 111 into an optical fiber FB1.

The light dividing means 3 comprises, for instance, a 2×2 fiber opticcoupler and divides the light beam La led thereto by way of the opticalfiber FB1 from the light source unit 210 into the measuring light beamL1 and the reference light beam L2. The light dividing means 3 isoptically connected to two optical fibers FB2 and FB3, and the measuringlight beam L1 is propagated through the optical fiber FB2 while thereference light beam L2 is propagated through the optical fiber FB3. Inthis embodiment, the light dividing means 3 also functions as themultiplexing means 4.

The optical probe 10 previously shown in FIG. 1 is optically connectedto the optical fiber FB2 and the measuring light beam L1 is guided tothe probe 10 from the optical fiber FB2. The probe 10 is inserted into abody cavity, for instance, through a forceps port by way of a forcepschannel and is removably mounted on the optical fiber FB2 by an opticalconnector 31.

The optical path length adjusting means 220 is disposed on the side ofthe optical fiber FB3 radiating the reference light beam L2. The opticalpath length adjusting means 220 changes the optical path length of thereference light beam L2 in order to adjust an initiating position of arange over which a tomographic image is to be obtained and comprises areflecting mirror 22 which reflects the reference light beam L2 radiatedfrom the optical fiber EB3, a first lens 21 a disposed between thereflecting mirror 22 and the optical fiber FB3, and a second lens 21 bdisposed between the first lens 21 a and the reflecting mirror 22.

The first lens 21 a makes parallel the reference light beam L2 radiatedfrom the core of the optical fiber FB3 and at the same time, collectsthe reference light beam L2 reflected by the reflecting mirror 2 on thecore of the optical fiber FB3. The second lens 21 b collects thereference light beam L2 made parallel by the first lens 21 a on thereflecting mirror 22 and at the same time, makes parallel the referencelight beam L2 reflected by the reflecting mirror 22. That is, the firstand second lenses 21 a and 21 b form a confocal optical system.

Accordingly, the reference light beam L2 radiated from the optical fiberFB3 is turned to a parallel light by the first lens 21 a and iscollected on the reflecting mirror 22 by the second lens 21 b.Subsequently, the reference light beam L2 reflected by the reflectingmirror 22 is turned to a parallel light by the second lens 21 b and iscollected on the core of the optical fiber FB3 by the first lens 21 a.

The optical path length adjusting means 220 is further provided with abase portion 23 to which the second lens 21 b and the reflecting mirror22 are fixed and a mirror movement means 24 which moves the base portion23 in the direction of the optical axis of the first lens 21 a. Inresponse to movement of the base portion 23 in the direction of arrow A,the optical path length of the reference light beam L2 can be changed.

The multiplexing means 4 comprises a 2×2 fiber optic coupler asdescribed above, and multiplexes the reference light beam L2 which hasbeen shifted in its frequency and has been changed in its optical pathlength by the optical path length adjusting means 220 and the reflectedlight beam L3 from the object Sb to emit the multiplexed light beamtoward the interference light detecting means 240 by way of an opticalfiber FB4.

The interference light detecting means 240 detects interference light L4of the reflected light beam L3 and the reference light beam L2 whichhave been multiplexed by the multiplexing means, and comprises acollimator lens 141 which makes parallel the interference light beam L4radiated from the optical fiber FB4, a spectral means 142 which dividesthe interference light beam L4 having a plurality of wavelength bands bythe wavelength bands and a light detecting means 144 which detects eachwavelength band of the interference light beam L4 divided by thespectral means 142.

The spectral means 142 comprises, for instance, a diffraction gratingelement, and spectrally divides the interference light beam L4 enteringit to output the divided interference light beam L4 to the lightdetecting means 144. The light detecting means 144 is formed by, forinstance, a CCD element which comprises a plurality of, for instance,one-dimensionally or two-dimensionally arranged photosensors and each ofthe photosensors detects each wavelength band of the interference lightbeam L1 spectrally divided as described above.

The light detecting means 144 is connected to an image obtaining means250 comprising, for instance, a computer system such as a personalcomputer. The image obtaining means 250 is connected to a display system260 formed, for instance, by a CRT or a liquid crystal display system.

Operation of the optical tomography system 1 having a structuredescribed above will be described, hereinbelow. When a tomographic imageis to be obtained, the optical path length is first adjusted by movingthe base 23 in the direction of the arrow A so that the object Sb ispositioned in the measurable area. The light beam La is emitted from thelight source unit 210 and the light beam La is divided into themeasuring light beam L1 and the reference light beam L2 by the lightdividing means 3. The measuring light beam L1 is radiated from theoptical probe 10 toward a body cavity and is projected onto the objectSb. At this time, the measuring light beam L1 radiated from the opticalprobe 10 is caused to one-dimensionally scan the object Sb by theoptical probe 10 operating as described above. Then the reflected lightbeam L3 from the object Sb and the reference light beam L2 reflected bythe reflecting mirror 22 are multiplexed, and the interference lightbeam L4 of the reflected light beam L3 and the reference light beam L2is detected by the interference light detecting means 240. Informationon the intensity distribution of the reflected light in the direction ofdepth of the object Sb is obtained by carrying out frequency analysis onthe detected interference light beam L4 in the image obtaining means 50after carrying out a suitable waveform compensation and noise removal.

By causing the measuring light beam L1 to scan the object Sb by theoptical probe 10 as described above, information on the direction ofdepth of the object Sb along the direction of scan is obtained andaccordingly tomographic images on the cross-section including thedirection of scan can be obtained. The tomographic images thus obtainedare displayed by the display system 260. Further, for instance, bymoving the optical probe 10 right and left in FIG. 5 so that themeasuring light L1 scans the object Sb in a second directionperpendicular to said direction of scan, tomographic images on thecross-section including the second direction can be further obtained.

Another example of the optical tomography system to which the opticalprobes of the present invention are to be applied will be described,hereinbelow. The optical tomography system 300 shown in FIG. 6 is forobtaining a tomographic image of the object of measurement by measuringthe SS-OCT and specifically differs from the optical tomography system 1shown in FIG. 5 in that structure of the light source unit and theinterference light detecting means.

The light source unit 310 of this system emits a laser beam La whilesweeping its wavelength at a predetermined period. Specifically, thelight source unit 310 comprises a semiconductor optical amplifier (asemiconductor gain medium) 311 and an optical fiber FB10 connected tothe semiconductor optical amplifier 311 at opposite ends thereof. Thesemiconductor optical amplifier 311 emits weak light to one end of theoptical fiber FB10 in response to injection of a drive current andamplifies light input from the other end of the optical fiber FB10. Whena drive current is supplied to the semiconductor optical amplifier 311,a pulse-like laser beam La is emitted to the optical fiber FB1 by aresonator formed by the semiconductor optical amplifier 311 and theoptical fiber FB10.

Further, an optical divider 312 is connected to the optical fiber EB10and a part of the light beam propagated through the optical fiber FB10is emitted from the optical divider 312 toward the optical fiber EB11.Light emitted from the optical fiber EB11 travels through the collimatorlens 313, the diffraction grating 314 and the optical system 315 and isreflected by the rotating polygon mirror 316. The reflected light isreturned to the optical fiber FB11 by way of the optical system 315, thediffraction grating 314 and the collimator lens 313.

The rotating polygon mirror 316 rotates in the direction indicated byarrow RH, to vary the angle of each reflective surface thereof withrespect to the optical axis of the optical system 315. Thereby, only alight beam having a specific frequency, from among the light spectrallysplit by the diffraction grating 314, is returned to the optical fiberFB11. The frequency of the light beam that reenters the optical fiberFB11 is determined by the angle formed by the optical axis of theoptical system 315 and the reflective surface of the rotating polygonmirror 316. Then the light beam of a specific frequency band impingingupon the optical fiber FB5L enters the optical fiber FB10, and as aresult, only a laser beam La of the specific frequency band is emittedtoward the optical fiber FB1.

Accordingly, when the rotating polygon mirror 316 rotates in thedirection indicated by arrow R1 at a constant speed, the wavelength A ofthe light beam which reenters the optical fiber FB11 changes at a periodwith time. As a result, a laser beam La which is swept in its wavelengthis emitted from the light source unit 310 toward the optical fiber FB1.

The interference light detecting means 240 detects interference lightbeam L4 of the reflected light beam L3 and the reference light beam L2which have been multiplexed by the multiplexing means 4 and the imageobtaining means 250 detects the intensities of the reflected light beamL3 in positions in the direction of depth of the object Sb by carryingout frequency analysis on the interference light beam L4 detected by theinterference light detecting means 240 and obtains a tomographic imageof the object Sb. The tomographic images thus obtained are displayed bythe display system 260. In this embodiment, a mechanism where theinterference light L4 is divided into a pair of lights which are guidedto optical detectors 40 a and 40 b and a balanced detection is carriedout in a calculating means 241 is formed. As can be understood, in thisembodiment, the interference light detecting means 240 is formed by theoptical detectors 40 a and 40 b and the calculating means 241.

Here, detection of the interference light beam L4 in the interferencelight detecting means 240 and image generation in the image obtainingmeans 250 will be described briefly. Note that a detailed description ofthese two points can be found in “Optical Frequency ScanningInterference Microscopes”, M. Takeda, Optics Engineering Contact, Vol.41, No. 7, pp. 426-432, 2003.

When the measuring light beam L1 is projected onto the object Sb, thereflected light L3 from each depth of the object Sb and the referencelight L2 interfere with each other with various optical path lengthdifference l. When the light intensity of the interference fringe atthis time versus each optical path length difference is assumed to beS(l), the light intensity I(k) detected in the interference lightdetecting means 240 is expressed by the following formula.I(k) = ∫₀^(∞)S(l)[l + cos (kl)]𝕕lwherein k represents the wave number and l represents the optical pathlength difference. The above formula may be considered to be given as aninterferogram of a light frequency range having a wave number of ω/c(k=ω/c) as a variable. Accordingly, a tomographic image is generated byobtaining in the image obtaining means 250 information on the distanceof the object Sb from the measurement initiating position andinformation on the intensity of reflection by carrying out frequencyanalysis by Fourier-transform on the spectral interference fringesdetected by the interference light detecting means 240 and determiningthe intensity S(l) of the interference light beam L4.

In the optical tomography system 300, an optical probe 10 the same inarrangement as that employed in the system of FIG. 5 is employed and theoperation is the same as that employed in the system of FIG. 5.

Still another example of the optical tomography system to which theoptical probes of the present invention are to be applied will bedescribed, hereinbelow. The optical tomography system 400 shown in FIG.7 is for obtaining a tomographic image of the object of measurement bymeasuring the TD-OCT and comprises a light source unit 210 provided witha light source 111 which emits laser light La and a light collectinglens 112, a light dividing means 2 which divides a laser light Laemitted from the light source unit 210 and propagated through theoptical fiber FB1, a light dividing means 3 which divides the laserlight La passing therethrough into measuring light L1 and referencelight L2, an optical path length adjusting means 220 which adjusts theoptical path length of the reference light L2 divided by the lightdividing means 3 and propagated through the optical fiber FB3, anoptical probe 10 which projects onto the object Sb the measuring lightL1 divided by the light dividing means 3 and propagated through theoptical fiber FB2, a multiplexing means 4 (the light dividing means 3doubles) which multiplexes the reflected light L3 from the object Sbwhen the measuring light L1 divided by the light dividing means isprojected onto the object Sb and the reference light L2, and aninterference light detecting means 240 which detects interference lightL4 of the reflected light L3 and the reference light L2 which have beenmultiplexed by the multiplexing means 4.

The optical path length adjusting means 220 comprises a collimator lens21 which makes parallel the reference light beam L2 radiated from theoptical fiber FB3, a reflecting mirror 23 which is movable in thedirection of arrow A to change the distance from the collimator lens 21,and a mirror moving means 24 which moves the reflecting mirror 23 andchanges the optical path length of the reference light L2 in order tochange the measuring position in the object Sb in the direction ofdepth. The reference light L2 which has been changed in its optical pathlength by the optical path length adjusting means 220 is guided to themultiplexing means 4.

The interference light detecting means 240 detects the intensity of theinterference light L4 propagating through the optical fiber FB2 from themultiplexing means 4. Specifically, only when the optical lengthdifference between the sum of the total optical path length of themeasuring light L1 and the optical path length of the reflected light L3reflected or scattered rearward at a certain point on the object Sb andthe reference light L2 is smaller than the coherence length of the lightsource, an interference signal whose amplitude is proportional to theamount of the reflected light is detected. Further, as the optical pathlength is scanned by the optical path length adjusting means 220, theposition of the reflecting point (depth) in which the interferencesignal is obtained is changed, whereby the interference light detectingmeans 240 detects a reflectance signal in each measuring position ofobject Sb. Information on the measuring position is output from theoptical path length adjusting means 220 to the image obtaining means. Onthe basis of the signals detected by the interference light detectingmeans 240 and information on the measuring-position in the mirror movingmeans 24, information on the intensity distribution of the reflectedlight in the direction of depth of the object Sb is obtained by theimage obtaining means 250.

By causing the measuring light beam L1 to scan the object Sb by theoptical probe 10 as described above, information on the direction ofdepth of the object Sb is obtained and accordingly tomographic images onthe cross-section including the direction of scan can be obtained. Thetomographic images thus obtained are displayed by the display system260. Further, for instance, by moving the optical probe 10 right andleft in FIG. 5 so that the measuring light L1 scans the object Sb in asecond direction perpendicular to said direction of scan, tomographicimages on the cross-section including the second direction can beobtained.

In the optical tomography system 400, an optical-probe 10 the same inarrangement as that employed in the system of FIG. 5 is also employedand the operation is the same as that employed in the system of FIG. 5.

Though the optical tomography systems 1, 300 and 400 in which theoptical probe 10 is employed, the optical probes 100 in accordance withpreviously described other embodiments of the present invention may be,of course, employed instead of the optical probe 10.

1. An optical probe comprising a tubular outer envelope, a optical fiberwhich extends in the longitudinal direction of the outer envelope insidethe outer envelope, a drive means which rotates the optical fiber in thecircumferential direction of the outer envelope, a light deflectingelement which is integrally held to rotate together with the opticalfiber and deflects light emitted from a front end of the optical fiber,a light collecting means which collects light emitted from the front endof the optical fiber and converges it on a body-to-be-scanned disposedexternally of the circumference of the outer envelope, a protectivemember which has a higher resistance to wear than the outer peripheralsurface of the optical fiber, and is fixed to a part of the outerperipheral surface of the optical fiber in a position near the front endof the optical fiber, and a bearing portion which is fixed to the innerperipheral surface of the probe outer envelope to bear for rotation theoptical fiber by way of the protective member.
 2. An optical probe asdefined in claim 1 in which the outer peripheral surface of the opticalfiber is formed by the resin and the protective member is formed ofmetal.
 3. An optical probe as defined in claim 1 in which the protectivemember is provided with an abutment portion which abuts against a partof the bearing portion to suppress the movement of the protective memberin the direction of axis of the optical fiber.
 4. An optical probe asdefined in claim 2 in which the protective member is provided with anabutment portion which abuts against a part of the bearing portion tosuppress the movement of the protective member in the direction of axisof the optical fiber.
 5. An optical tomography system for obtaining atomographic image of an object to be measured comprising a light sourcewhich emits light, a light dividing means which divides light emittedfrom the light source into measuring light and reference light, aprojecting optical system which projects the measuring light onto theobject, a multiplexing means which multiplexes the reflected light fromthe object when the measuring light is projected onto the object and thereference light, an interference light detecting means which detectsinterference light of the reflected light and the reference light whichhave been multiplexed by the multiplexing means, and a tomographic imageobtaining means which detects intensities of the interference light inpositions in the direction of depth of the object on the basis of thefrequency and intensity of the detected interference light and obtains atomographic image of the object on the basis of the intensity of thereflected light in each position of the depth, wherein the improvementcomprises that the projecting optical system includes an optical probecomprising a tubular outer envelope, a optical fiber which extends inthe longitudinal direction of the outer envelope inside the outerenvelope, a drive means which rotates the optical fiber in thecircumferential direction of the outer envelope, a light deflectingelement which is integrally held to rotate together with the opticalfiber and deflects light emitted from a front end of the optical fiber,a light collecting means which collects light emitted from the front endof the optical fiber and converges it on a body-to-be-scanned disposedexternally of the circumference of the outer envelope, a protectivemember which has a higher resistance to wear than the outer peripheralsurface of the optical fiber, and is fixed to a part of the outerperipheral surface of the optical fiber in a position near the front endof the optical fiber, and a bearing portion which is fixed to the innerperipheral surface of the probe outer envelope to bear for rotation theoptical fiber by way of the protective member..
 6. An optical tomographysystem as defined in claim 5 in which the outer peripheral surface ofthe optical fiber is formed by the resin and the protective member isformed of metal.
 7. An optical tomography system as defined in claim 5in which the protective member is provided with an abutment portionwhich abuts against a part of the bearing portion to suppress themovement of the protective member in the direction of axis of theoptical fiber.
 8. An optical tomography system as defined in claim 6 inwhich the protective member is provided with an abutment portion whichabuts against a part of the bearing portion to suppress the movement ofthe protective member in the direction of axis of the optical fiber.